Integrating silicon detectors in a photonic chip

Quantum photonic integrated circuits (PICs) exploit the virtually null photon-photon interaction to realize systems that are robust to external disturbance. While this resilience is particularly interesting for a development towards room-temperature systems, many experiments rely on superconducting nanowires that need cryogenic temperatures to operate. For photons in the near infrared spectral region, single photon avalanche diodes (SPADs) could be used as a room temperature alternative. We show a novel method of PIC-detector coupling that allows for the monolithic fabrication of substrate-integrated photodiodes and a silicon nitride PIC on the same chip. With the use of an engineered wet-etching process, we shape the bottom cladding of the photonic layer into a basin with shallow wedge borders on top of the region of the detectors. In this way, the waveguides are gently laid on top of the detectors, allowing for a strong waveguide-detector optical coupling. We show experimental results of the first PIC-diode coupling with a total efficiency exceeding 40%, and the first promising results concerning the coupling with SPADs paving the way for on-chip, room-temperature, single photon detection.